Method for producing thin layers on a specific support and an application thereof

ABSTRACT

The invention relates to a method for producing a thin layer ( 8 ) containing at least one component ( 6, 6 A,  6 B) comprising:—a preparation step, wherein an added layer ( 2, 3, 4 ) is created on a support ( 1 ), at least one part ( 2 ) of said layer being adapted for local embrittling and said substrate and the part which can be embrittled being made from different materials and/or having different microstructures; an embrittlement step, wherein a fragile underlayer ( 5 ) is produced in the part which can be embrittled; a work step, wherein at least one component ( 6, 6 A,  6 B) is created on said added layer; and a separation step, wherein a dissociation is induced in the part which can be embrittled, along said fragile underlayer, in order to produce a thin layer ( 8 ) comprising a part of said added layer and said component.

FIELD

[0001] Future portable systems (for example mobile telephones, chipcards or personal organizers of the future) will integrate an increasingnumber of functions. These systems, for example personal organizers ofthe future, will use a number of technological <<modules>>. Thesetechnological modules include: screens, operating system,microprocessor, batteries. Of these components, the screens are the oneswhich occupy the greater part of the surface area and their integrationin the system is an important aspect.

[0002] These objects will not be developed on a mass scale unless thecost of these components comes down. For this to happen, it is necessaryto find technologies that are compatible with high volumes, enablingthese components to be made on substrates of large dimensions, such asglass for example. However, although this substrate is not expensive, ithas a major drawback, namely its resistance to shock. Components ordevices made on these substrates necessarily require the use ofadditional protective measures if they are to be integrated in portablesystems.

[0003] To integrate these components in the most efficient way possible,it would be practical if these components could be integrated on thefinal substrate. In many situations, it may be of advantage to useplastic for this substrate. One of the challenges this presents, forexample, is to make screens on a plastic substrate, combining theadvantages of low cost, low weight and high resistance to shock (atleast compared with glass). This application is of particular interestin the case of new generation mobile telephones.

[0004] In mobile systems, such as chip cards for example, it is alsonecessary to have components of a slim thickness (to adapt to that ofthe chip card), in order to deal with the problems of weight andflexibility.

PROBLEM TO BE SOLVED

[0005] Making these components on a substrate such as plastic is adelicate matter. In practice, it is necessary either to modify theentire technology used to make these components, rendering it compatiblewith the use of conventional plastic, or to find special <<plastic>>substrates that are compatible with the heat treatments used with thetechnology (it is clear, in particular, that it will be necessary towork below the softening point of these substrates).

[0006] Another approach is to make the components (integrated circuits,screens, passive components) on a substrate that is compatible withexisting technologies and then transfer them to their final substrates.

[0007] The interest of this approach is that it allows certaincomponents to be made on low-cost substrates using technologies that areoften simpler than the technologies used as standard inmicroelectronics. Examples of this are the technologies used to makeflat screens, such as thin film transistors known under the acronym TFT,which are made from amorphous or polycrystalline silicon. Thesetechnologies involve the use of glass substrates as a rule.

[0008] Different techniques may be used to transfer layers from onesubstrate to another substrate. The techniques published in 1985 by T.Hamaguchi et al.—Proc. IEDM 1985 p. 688 are examples of these. Thesetechniques are of particular interest because they provide an efficientway of transferring a layer from one substrate to another but the basesubstrate is necessarily consumed (destroyed during processing) and thethin film cannot be transferred homogeneously (i.e. with a constantthickness at every point) unless a barrier layer is used in order toprevent the substrate from being consumed.

[0009] More recently, other techniques for transferring TFT transistors(made from polysilicon on a glass substrate) onto plastic substrateshave become known. Ref. S. Utsunomiya et al.—Proc. IDS 2000 p. 916 orpatent EP 0 924 769 Al by Seiko. These methods are based on an approachaccording to which a separation layer (generally of amorphous silicon)is created on a substrate and, once the components have been made onthis layer, they can then be separated and transferred to anothersubstrate. In this case, the separation (or exfoliation) is effectedusing light irradiation (typically a laser-type beam). However,radiation of this type is difficult to control when working with largesurfaces. In practice, if illumination is not homogeneous, it can leadto a non-homogeneous exfoliation, which can cause deterioration in thesuperficial film. This is a not inconsiderable technical handicap.

[0010] Of the various transfer methods, it is also possible to usemethods of the type used to transfer thin layers of materials, which mayor may not contain a microelectronic component, either in their entiretyor a part of them. These methods are based on creating a fragile layerembedded in a material by introducing one or more gaseous species.Reference may be made to documents U.S. Pat. No. 5,374,564 (orFR-A-2681472 or EP-A-533551), U.S. Pat. No. 6,020,252 (or FR-A-2748851or EP-A-807970), FR-A-2767416 (or EP-A-1010198), FR-A-2748850 (orEP-A-902843) or FR-A-2773261 (or EP-A-963598) which describe thesemethods.

[0011] These methods are generally used with a view to detaching theentire film from an initial substrate in order to transfer it to asubstrate. The thin film obtained then contains some of the substrate.These films may be used as active layers for making electronic oroptical components. In practical terms, the main advantage of theseprocesses is that they enable thin films of monocrystalline substratesto be applied to different substrates. These films may contain a wholecomponent or part of one.

[0012] With these processes, however, it is difficult to separate a thinlayer from certain substrates, such as glass, silica glass, ceramics,certain polymers and certain amorphous materials, etc. To achieve theseparation, it would be necessary to work under extreme experimentalconditions: very high implant dose and/or high mechanical energy forseparation purposes, etc. which barely seems feasible as things stand atpresent.

[0013] Glass is a substrate with a number of advantages. It isinexpensive, comes in large dimensions and is easy to manipulate. It isvery widely used as a substrate for components such as active matricesand reading circuits for flat screens, color filters and even certainpassive components (R, L, C).

[0014] A particular object of the invention is to take components madeon this type of substrate and transfer them onto another substrate (forexample plastic) or transfer them onto another substrate without havingto create a fragile layer in the first substrate on which the componentsapplied to it are picked up.

[0015] More generally, an object of the invention is to propose a methodaccording to which components or devices made on a first substrate canbe transferred to another substrate, without the drawbacks inherent inall the existing methods (consumption of the substrate, lack ofhomogeneity resulting from the transfer, specific properties of thesubstrate). In particular, an object of the invention is to be able topick up components or devices made on a substrate which does notnormally lend itself to producing an embedded layer that is weakened(the substrate can be recycled and reused once the film containing allor some of the components has been recovered) and to enable a veryhomogeneous transfer onto large dimensions (several tens ofcentimeters).

PRESENTATION OF THE INVENTION

[0016] To this end, the invention proposes a method for producing a thinlayer incorporating at least a part of a component, comprising:

[0017] a preparation step according to which an added layer is appliedto a first substrate, at least a part of which is such that it can belocally weakened, this substrate and this part which can be weakenedbeing made from different materials and/or having differentmicrostructures,

[0018] a weakening step according to which a fragile sub-layer iscreated in this part which can be weakened,

[0019] a work step during which at least all or part of a component ismade on this added layer, and

[0020] a separation step according to which a separation is caused inthis weakened part and along this fragile sub-layer so as to obtain athin layer incorporating a part of this added layer and this componentpart.

[0021] Accordingly, the invention enables a thin layer incorporating acomponent to be separated from a substrate which can be freely selectedaccording to various criteria relating to the preparation of thiscomponent, without having to make provision for effecting thisseparation in this substrate.

[0022] The invention applies more particularly to substrates which donot easily lend themselves to applications requiring a weakened layer tobe provided with a view to subsequent separation. Consequently, theinvention applies in particular to situations where the substrate ismade from a semiconductor material or glass or silica glass (othermaterials also have the same drawback, especially ceramics, certainpolymers and certain amorphous materials etc., see above), or substrateswhich enable separation but under conditions more difficult than thoseunder which the detachable layer can be applied.

[0023] The invention applies more specifically to the situation where itis desirable to obtain a thin layer of large dimensions (which naturallymeans that the substrate must be of at least the same dimensions), inwhich case it is necessary in practical terms to use a substrate withgood mechanical strength, in particular good rigidity.

[0024] The added layer may be of various types. For example, it may bemade of silicon (preferred case), or even from germanium or an alloy ofsilicon and germanium. If this layer is made from silicon, it may bepolycrystalline by preference, which is less expensive thanmonocrystalline silicon.

[0025] The part which can be weakened is advantageously made bydeposition followed by recrystallisation. However, it may be made byother processes such as those described in patent specification U.S.Pat. No. 5,374,564.

[0026] This part which can be weakened is typically of the order of atleast 50 manometers thick and is preferably less than about 1000manometers: this helps to obtain good flatness in the bottom surface ofthe thin layer.

[0027] A priming layer may or may not be disposed between the substrateand the part which can be weakened. If the substrate is made from glassor silica glass and the part to be weakened is made from silicon, apriming layer of silicon oxide may optionally be applied.

[0028] According to another advantageous characteristic of theinvention, the added layer has an additional layer on the part to beweakened, which receives the component (or at least part of it) and isidentical or similar in nature (in terms of composition and mechanical,chemical properties, etc.) to that of the substrate. If this substrateis made from glass or silica glass, this additional layer isadvantageously silicon oxide.

[0029] This additional layer may be added prior to or after theweakening step.

[0030] Accordingly, this characteristic of the invention involves makingthe weakened layer within a <<quasi-substrate>> (it is sandwichedbetween two identical or very similar materials); the latter has all theadvantages offered by a substrate (for example: surface state, overallrigidity in the case of glass) whilst readily lending itself to thecreation of a layer which is weakened by introducing gaseous speciesinto the sandwiched layer. This <<quasi-substrate>> enables componentsor devices to be made on an incompatible substrate affording easyseparation and then separating them without any problems, with a view totransferring them to another substrate.

[0031] The additional layer is preferably of the order of from 300manometers to 10000 manometers thick, which is sufficiently thin topermit the weakening process but enough to be of significance to allowthe component(s) or at least part of them to be made and/or to enablethe thin layer to be rendered self-supporting and/or to avoid theoccurrence of blistering during the steps involved in making thesecomponents, weakening or separation. In other words, this additionallayer, located between the layer to be weakened and the components, mayserve as a stiffener for the resultant thin layer. This also means thatthe thin layer can be manipulated before being placed on a finalsubstrate, obviating the need for a temporary substrate.

[0032] This additional layer is preferably thicker than the layer to beweakened (for the reasons mentioned above in respect of the thickness ofthis layer to be weakened and the additional layer).

[0033] Advantageously, a third layer may be provided underneath theadditional layer (between this additional layer and the layer to beweakened) which will ensure that the layer incorporating the componentsis compatible with the final substrate. This third layer may be a layerof Si3N4, for example. This being the case, after fracturing at thelevel of the weakened zone, the remaining part of the detachable layeris removed in order to release the layer of Si3N4.

[0034] The weakening step advantageously includes applying a thermallyactivatable treatment. More specifically, this treatment preferablyincludes introducing elements deep in the layer to be weakened, whichcan then bring about the desired weakening on diffusion.

[0035] Accordingly, by virtue of one advantageous characteristic of theinvention, the weak zone is created by introducing gaseous species,preferably selected from hydrogen and/or helium and/or noble gases. Theuse of hydrogen is particularly appropriate; for more details, referencemay be made to documents U.S. Pat. No. 5,374,564 (or FR-A-2681472 orEP-A-533551), U.S. Pat. No. 6,020,252 (or FR-A-2748851 or EP-A-807970),FR-A-2767416 (or EP-A-1010198), FR-A-2748850 (or EP-A-902843) orFR-A-2773261 (or EP-A-963598).

[0036] If opting for this type of thermally activatable treatment, theseparation step preferably involves a specific input of thermal energy.

[0037] To be truly effective, this input preferably has the effect ofraising at least the part to be weakened to a thermal budget in excessof the thermal budget already applied during the step when thecomponents were manufactured.

[0038] The separation treatment may include an input of mechanicalenergy (in the broadest sense of the term, i.e. in the form of forcesapplied or constraints induced in the structure but also in pneumaticform, for example by an injection of gas, etc.) used in combination withthe above-mentioned application of heat energy or alone.

[0039] In certain cases where several components or devices are made ona same substrate, it may be of advantage to produce a localizedseparation on a zone, the size of which corresponds to that of a device(or a whole number of devices).

[0040] By preference, object of the method proposed by the invention isto make an array of active or passive elements intended to contributejointly to a same function; such an array is conventionally called a<<device>>. By way of example, a device may contain an optical,optoelectronic, electronic component, colored filters or a mechanical,chemical and/or biological sensor . . . It may also be a matrix with itsaddress circuit (as in the case of a flat screen). A device thereforeessentially consists of more than one component; and the componentspresent within a layer are not necessarily identical.

[0041] Accordingly, a distinction may be made between several specific(but not exclusive) situations depending on whether the manufacturingstep includes the manufacture:

[0042] of an optical or optoelectronic component,

[0043] and/or an electronic component,

[0044] and/or a mechanical, chemical or biological sensor.

[0045] One case of particular interest is that in which themanufacturing step includes at least the manufacture of at least oneactive matrix and its address circuit, designed to be integratedsubsequently within a flat screen.

[0046] The method proposed by the invention may also include a coveringstep, after the work step, according to which a protective layer isdeposited on the added layer incorporating the component. Thisprotective layer is preferably made from silicon nitride, Si3N4, atleast if the added layer is made from silicon and/or is an additionallayer of silicon oxide. This protective layer may act as a means ofensuring compatibility with a final substrate (for example preventingthe deterioration of components on a plastic substrate).

[0047] The transfer of all or part of the thin layer to a finalsubstrate (or to several final substrates if the thin layer is notintended for a single final substrate) may or may not require the use ofan intermediate substrate.

[0048] The method proposed by the invention may also include, before theseparation step, a joining step according to which an intermediatesubstrate is affixed to the added layer (including the additional layerif one is provided) and, after the separation step, a step according towhich this intermediate substrate is used to affix all or part of thethin layer to the final substrate(s).

[0049] During this joining step, the thin layer is preferably affixed tothe intermediate substrate in a reversible manner and the thin layer isdetached from the intermediate substrate after the transfer step. It isvery easy to detach the detachable part of the thin layer from theintermediate substrate without the need for any specific treatment.

[0050] The final substrate is advantageously made from a differentmaterial than that used for the initial substrate. In particular, thefinal substrate may be a material that is incompatible with the thermalconditions which prevail during the work step or those during theseparation step; this significantly broadens the choice available forthis final substrate. Accordingly, it may advantageously be of a plasticmaterial, for example transparent, the softening temperature of whichmay be lower than the maximum temperature of the work step (which issuch that this substrate would not withstand this step); in practicalterms, this is a situation of particular interest.

[0051] In this respect, the invention covers the specific application ofthe process involved in making flat screens.

[0052] It should be pointed out that the final substrate may be ofdifferent dimensions than the initial substrate and hence the resultantthin layer (bigger or smaller, depending on requirements).

[0053] Another case of particular interest is one where the finalsubstrate is a chip card or a part of a mobile telephone, or even theplastic polarizer of a self-supporting flexible screen.

[0054] At this stage, it is important to note that if a plurality ofcomponents are provided on the added layer or additional layer duringthe work step, each component may be individually affixed to a specificfinal substrate, for example a chip card, having been detached from therest of the thin layer (this comment also applies to the situation wherethe manufacturing step consists in making a plurality of batches ofcomplementary components: each batch can be individually deposited).

[0055] An intermediate substrate of this type may be used to generatemechanical stresses at the level of the weakened layer in order todetach the thin layer from the substrate.

[0056] It should also be pointed out that the use of such anintermediate substrate for transferring to a final substrate separatefrom the initial substrate is not necessary in the case described abovewhere an additional layer is thick enough to fulfill a stiffeningfunction.

[0057] Another variant of the method proposed by the invention consistsin incorporating a joining step, before the separation step, accordingto which the added layer (including the additional layer if one isprovided) is affixed to a final substrate. In this case, the componentswill be disposed on this final substrate in a layout that is the inverseof the layout of these components on the added layer (the layout ofcomponents is maintained if the transfer is made via an intermediatesubstrate; and this layout may be maintained or inverted, as required,if the thin layer is self-supporting, i.e. if the additional layer actsas a stiffener.

[0058] Any means may be used to affix the component(s), with or withoutthe rest of the thin layer, in particular bonding by means of anadhesive or alternatively by molecular adhesion.

[0059] The objectives, characteristics and advantages of the inventionwill become clear from the description below, given by way ofnon-limitative illustrative example, with reference to the appendeddrawings, in which:

[0060]FIG. 1 is a schematic view in section of a substrate, on which acompatibility (priming) layer and then an added layer in two parts havebeen deposited during a preparatory step,

[0061]FIG. 2 is a view of this substrate after a weakening step,

[0062]FIG. 3 is a view of this substrate after a step during whichcomponents were manufactured,

[0063]FIG. 4 is a view of this substrate after a detachment step,

[0064]FIG. 5 is a view of a similar substrate after a step during whichit was joined to a substrate,

[0065]FIG. 6 is a view of this second substrate after a detachment step,

[0066]FIG. 7 is a view of the thin layer resulting from the stepillustrated in FIG. 6, after a partial transfer step

[0067]FIG. 8 is a view in section of a pane of glass to which a layerhas been transferred in two parts,

[0068]FIG. 9 is a view of this pane after making components of a firsttype,

[0069]FIG. 10 is a view of a pane similar to that illustrated in FIG. 8after making components of a second type,

[0070]FIG. 11 is a view of the two panes illustrated in FIGS. 9 and 10after partial detachment and fixing in a head to tail configuration,

[0071]FIG. 12 is a view in section along line XII-XII indicated in FIG.11,

[0072]FIG. 13 is a view illustrating a step during which the bottom paneis cut,

[0073]FIG. 14 is a view in section along line XIV-XIV indicated in FIG.13,

[0074]FIG. 15 is an overall view after cutting as illustrated in FIGS.13 and 14 and transferring to a plastic substrate, showing the contourof a step during which the top plate is cut,

[0075]FIG. 16 is a view of a component after cutting and transfer to asecond plastic substrate, and

[0076]FIG. 17 is a view of this component in section.

[0077] FIGS. 1 to 4 provide general illustrations of an example of howthe method proposed by the invention is implemented.

[0078] A pane of glass 1 of large dimensions, such as those used tomanufacture LCD screens, for example, is the starting material. Forexample, it is a glass sold by the CORNING company under reference 1737.

[0079] A layer 2 of amorphous silicon is deposited in a thickness of 300nm, for example, which is recrystallised by means of a laser beam toobtain polycrystalline silicon, also known as polysilicon. As willbecome clear below, this layer 2 can be weakened. Monocrystallinesilicon can also be transferred but is not as interesting from aneconomic point of view.

[0080] In certain cases, before creating this layer specificallyintended to permit detachment of a thin layer, an intermediate layer 3may be deposited on the substrate to improve adhesion. This priminglayer 3 might be a layer of silicon oxide, for example. The thickness ofthis layer is exaggerated in FIG. 1 to make it visible; this thicknessmay be barely 10 manometers.

[0081] The layer of polysilicon may also be obtained by CVD depositionat a temperature of 550° C., for example. This variant may be preferableto the one described above if the substrate is silica glass and if thesubstrate is capable of withstanding temperatures in the range of thedeposition temperature. It should be pointed out that an expensivesubstrate may be used for the method proposed by the invention becausein one embodiment this substrate can be recycled (is not consumed).

[0082] In the example illustrated, a layer 4 of silicon oxide a fewhundred manometers thick (for example 800 nm) is then deposited toreturn to a free surface of the SiO2 type close to that of the initialglass. Consequently, a quasi substrate 1+2+4 or 1 and 4 is obtained,made of very similar materials.

[0083] As illustrated in FIG. 2, a fragile sub-layer 5 is created in thelayer 2. To this end, a treatment is applied which can then be thermallyactivated. By preference, ions or gaseous elements (they amount to thesame thing, insofar as the lightest ions are ions of a gaseous element)are introduced at a depth in the polysilicon layer to create a layerwhich is weakened or will subsequently cause the detachment. Forexample, hydrogen is implanted in a dose of the order of 7E16H+/cm² andan energy of 100 keV.

[0084] These separation treatments will be adapted depending on theweakening steps (implantation dose, energy, implantation temperatureetc.).

[0085] A silicon oxide layer of 3 micrometers thickness may be deposited(in the example described, therefore, this is tantamount to thethickness of the layer 4) to obtain a self-supporting structure afterdetachment. This layer will serve as a stiffener in the thin layerproduction process.

[0086] All or part of a device, i.e. at least one component 6 (there arethree in FIG. 3, denoted by 6, 6A and 6B, which may jointly constitute adevice) is then made on the SiO2 surface (see FIG. 3). This step isoperated under conventional conditions, such as those which apply ifworking with a substrate made entirely of glass.

[0087] If the ultimate aim is to obtain a flat screen, the device may bemade up of transistor units in the active matrix and its addresscircuit. As a rule, this technology does not require a temperature inexcess of about 400° C.

[0088] A separation treatment (which is continued until detachment isachieved) is then applied to induce the transfer—see FIG. 4. As a rule,this step may include a heat treatment and/or a mechanical treatment. Incertain cases, this separation may be initiated by a first means (forexample heat) and then propagated to the detachment stage, for exampleby cleaving, by a second means (which may be mechanical, for example).In another variant, a heat treatment may be applied for several minutesat approximately 450° C., for example, in order to bring about theseparation, followed by the detachment in the case where all the layersare capable of withstanding the heat treatment. The separation anddetachment conditions will largely depend on the implantation conditionsin a known manner.

[0089] The result is devices or components 6 which are separated fromtheir manufacturing substrate 1+2. The thin layer which is thus obtainedis denoted by reference 8. The spaces between the components may beoccupied by a protective substance.

[0090] By separate is meant that the devices may still be in contactwith the substrate but with a very low joining energy (held byelectrostatic forces, for example). The term detachment is used in thesense of complete separation to the degree that the thin layer 8 istotally separate from its substrate.

[0091] As stated above, the additional layer 4 was dimensioned to enableit to act as a stiffener, which means that the thin layer isself-supporting and no additional stiffener is required in order to beable to manipulate it. The components may therefore be transferred to afinal substrate (not illustrated).

[0092] Even though the thin layer may be said to be self-supporting,however, it may be preferable to adhere the device or the components 6to an intermediate substrate, which will enable it or them to bemanipulated more easily until the point at which it or they is or areplaced on the final substrate. Any means may be used to obtain suchadhesion, such as: the addition of a substance such as glue, forexample, or means for applying surface preparations (molecular adhesionin particular).

[0093] Accordingly, FIG. 5 illustrates a substrate similar to thatillustrated in FIG. 3, i.e. comprising a layer of glass 1′, a layer 2′which can be weakened (optionally incorporating a priming layer 3′) andan additional layer 4′ on which the components 6′, 6A′ et 6B′ areproduced. A protective layer, not illustrated, has advantageously alsobeen deposited. Before proceeding to detach the thin layer, thecomponents are affixed to a substrate 10. After detachment (see FIG. 6),the substrate 10 makes it easier to manipulate the components.

[0094] Accordingly, FIG. 7 shows the substrate from which the component6′ has been transferred, individually, and placed on a final substrate12, having been detached from the rest of the thin layer.

[0095] Another option might be one where it is desirable to place thecomponents directly in contact with their final substrate. This beingthe case, the intention is that the components will remain on thesubstrate.

[0096] Naturally, it may be that the substrate 10 does not have the samecomposition or the same properties, depending on whether it will be usedas a temporary substrate or the ultimate substrate.

[0097] If an intermediate substrate is used, adhesion can be controlledso that this adhesion is reversible. Consequently, once the device hasbeen joined to its final substrate, the intermediate substrate can beremoved.

[0098] It should be pointed out that a process of the type described inthe prior art publications may be used, which means in particular thatthe bonding forces are controlled by controlling the surface roughnessor hydrophilic properties.

[0099] After transferring the device to the final substrate, it may befinished by applying the relevant steps known from conventionaltechnology operating and compatible with the final substrate.

[0100] In one variant of the method, once the device (6′+6A′+6B′) hasbeen made, it is detached by means of a heat treatment followed by theuse of mechanical forces (applied by introducing a blade or introducinga liquid or gaseous fluid, etc., for example); the intermediatesubstrate 10 may help to generate forces within the fragile sub-layer,for example by applying torsional forces.

[0101] Such detachment can be obtained if the embedded fragile layer wasproduced by hydrogen implantation (6E16H+/cm2 at 100 keV). After makingthe device, at a temperature below 300° C. for example, a heat treatmentis applied for 30 minutes at 450° C. to produce a high degree ofweakening at the level of the fragile zone. Since this weakening givesrise to a thermally activated phenomenon, there is a specifictime-temperature correlation for each implantation condition (energy,dose).

[0102] Finally, the detachment is completed by mechanical means.

[0103] In the examples described above, the layer to be weakened issilicon. In another variant, this layer to be weakened might also begermanium, SiGe or any other material which can be weakened by ionimplantation (for example monocrystalline or polycrystallinesemiconductor).

[0104] Consequently, the method proposed by the invention may be used asa means of transferring a device (made entirely on a first substrate) toa second, for example of the plastic type. Accordingly, an entire LCDscreen can be made by conventional means and then finally transferred toa plastic substrate, which may advantageously be flexible.

[0105] FIGS. 8 to 17 illustrate the manufacture of a plurality of suchindividual LCD components.

[0106] In summary, this involves taking two panes of glass, which is theconventional approach to making flat screens: one pane on which thetransistors of the active matrix and the address circuit will be madeand one pane on which the color filters will be made. The two parts areassembled, the screen is finished, the glass substrate is removed andthe screen transferred to the final substrate. In one variant of themethod, the screen can be finished after being transferred to the finalsubstrate.

[0107]FIG. 8 illustrates one, 21A, of the initial panes (the sametreatment is applied to the other pane 21B). An added layerincorporating a layer to be weakened 22A (or 22B) is applied to eachpane as well as a top layer 24A (or 24B) which will act as a stiffener.

[0108] This layer to be weakened is advantageously made frompolycrystalline silicon (for example 200 nm). By preference, this layermay be even thinner (100 nm) in order to position the fracture in thisvery thin layer. A fragile zone is then created in this layer to permitsubsequent detachment at the level of this zone.

[0109] In the particular case described here, where several devices haveto be made on the same pane, it is of advantage to create fragile zonessolely at the level of the future devices. Accordingly, the objective isto obtain a zone that will be separated from the substrate at the levelof the components and held on the pane by the spaces between the devices(without a fragile zone). These fragile zones are denoted by references25A and 25B on the first and second panes in FIGS. 8 (and 9) and 10respectively.

[0110] The fragile zone is created by introducing a gaseous species, forexample by implanting hydrogen and/or helium ions. If hydrogen ions areused, the dose may be selected from within a range of between 3E16H+/cm²and 1E17H+/cm². The fragile zone at the level of the future devices maybe positioned by masking the zones that will not be implanted.

[0111] The layer 24A or 24B serving as a stiffener, for example an oxidelayer, can not be deposited until after this implantation. Its purposeis to permit separation without giving rise to blistering. Theconditions are such that the layer is self-supporting (seeFR-A-2738671).

[0112] For example, a layer of silicon oxide can be deposited to athickness of several microns, for example 5 microns, or even a thinlayer of fine glass can be deposited (for example 30 microns).

[0113] Having been prepared as above, these panes are put through allthe steps enabling the active matrix or color filter needed for the LCDcomponent to be made. FIG. 9 shows the pane 21A on which the elements ofthe color filter 26A have been made, whilst FIG. 10 illustrates the pane21B on which the elements of the active matrix 26B have been made (theyare TFT transistors or Thin Film Transistors and an element CA (standingfor address circuit)).

[0114] A treatment then follows to separate the thin layer, at the levelof the locally implanted zone, from the substrate or pseudo-substratewith a part of its device. This treatment is a heat treatment, forexample, operated at a temperature in the range of 450° C. to obtain alocal separation or a very extensive weakening to enable subsequentseparation using mechanical forces. In FIG. 11, the detachment zones aredistinguished from the weakened zone shown in FIGS. 9 and 10 by the factthat they are shown as continuous lines.

[0115] These two panes along with their components are then assembled bya conventional method with the aid of a line of glue. Provided this glueis compatible with the conditions prevailing during detachment, thelocal detachment may take place after assembly.

[0116]FIG. 11 shows the two panes mounted head to tail with across-piece 26C surrounding both each group of transistors TFT and eachcolor filter.

[0117] The conventional steps are then applied to obtain a LCD screen.i.e. filling with liquid crystal and sealing (see FIG. 12).

[0118] Then, as illustrated in FIGS. 13 and 14, the bottom pane is cutto the required dimensions, using the conventional diamond cuttingtechnique (known as <<scribe and break>>). The glass substrate is thenseparated from the rest of the component because it is then cutvertically (as a result of the above-mentioned detachment) and laterally(by the cutting process described above). It may be necessary to applymechanical force to obtain complete detachment at the level of theweakened zone.

[0119] Advantageously, all or part of the polycrystalline silicon layermay be removed before the transfer to the final substrate. In theexample illustrated in FIG. 15, the residual part of the polycrystallinesilicon has been removed in its entirety before gluing the componentonto the final substrate, in this case a plastic substrate 40. Theplastic substrate may advantageously be the polarizer. Its thickness maybe chosen to suit the intended application.

[0120] The cutting operation is then repeated on the top pane (FIG. 15)to finally obtain (see FIGS. 16 and 17) a LCD screen between twopolarizers 40 and 41 in the presence of the glass used to make it.

1. Method for producing a thin layer (8) incorporating at least a component part (6, 6A, 6B, 6′, 6A′, 6B′, 26A, 26B), comprising: a preparation step according to which an added layer (2, 3, 2′, 3′, 4, 4′, 22A, 22B) is made on a substrate (1, 1′, 21A, 21B), at least part (2, 2′) of which is such that it can be locally weakened, this substrate and this part to be weakened being made from different materials and/or having different microstructures, a weakening step, according to which a fragile sub-layer is (5, 5′, 25A, 25B) is created in this part to be weakened, a work step according to which at least this component part (6, 6A, 6B, 6′, 6A′, 6B′, 26A, 26B) is made on this added layer, and a separation step according to which this part to be weakened is made to detach along this fragile sub-layer in order to obtain a thin layer (8, 8′) incorporating a part of this added layer and this component part.
 2. Method according to claim 1, characterized in that the substrate (1, 1′) is made from semiconductor material or glass or silica glass.
 3. Method according to claim 1, characterized in that the substrate is made from an amorphous material.
 4. Method according to any one of claims 1 to 3, characterized in that the part to be weakened (2, 2′) in the added layer is made from at least one material selected from the group consisting of silicon, germanium and their alloys.
 5. Method according to claim 4, characterized in that the part to be weakened (2, 2′) in the added layer is made from silicon.
 6. Method according to claim 5, characterized in that this part to be weakened (2, 2′) is made from polycrystalline silicon.
 7. Method according to any one of claims 1 to 6, characterized in that the part to be weakened (2, 2′) is made by deposition followed by recrystallisation.
 8. Method according to any one of claims 1 to 7, characterized in that the part to be weakened (2,2′) is of a thickness of the order of 50 manometers to 1000 manometers.
 9. Method according to any one of claims 1 to 8, characterized in that the added layer (2, 2′, 3, 3′, 4, 4′) incorporates a sub-layer (3, 3′), the purpose of which is to prime the part to be weakened and the substrate.
 10. Method according to claim 9, characterized in that the substrate (1, 1′) is made from glass or silica glass, the part to be weakened (2, 2′) is made from silicon and the priming layer (3, 3′) is made from silicon oxide.
 11. Method according to any one of claims 1 to 10, characterized in that, on the part to be weakened, the added layer incorporates an additional layer (4, 4′), the nature of which is identical or similar to that of the substrate in terms of composition.
 12. Method according to claim 11, characterized in that the substrate is made from glass or silica glass and the additional layer is silicon oxide.
 13. Method according to claim 11 or claim 12, characterized in that the additional layer has a thickness of the order of 300 manometers to 10000 manometers.
 14. Method according to any one of claims 11 to 13, characterized in that the additional layer has a thickness which is thicker than that of the sub-layer to be weakened.
 15. Method according to any one of claims 1 to 14, characterized in that the weakening step includes applying a treatment which can be activated by heat.
 16. Method according to claim 15, characterized in that the weakening step includes introducing at least one gaseous species, selected from the group consisting of hydrogen, helium and noble gases, at a depth in the part to be weakened.
 17. Method according to claim 16, characterized in that the weakening step includes introducing hydrogen at a depth in the part to be weakened.
 18. Method according to any one of claims 1 to 17, characterized in that the separation step includes applying thermal energy.
 19. Method according to claim 18, characterized in that the effect of applying this thermal energy is to bring at least the part to be weakened to a thermal budget in excess of the thermal budget already applied.
 20. Method according to any one of claims 1 to 19, characterized in that the separation step includes applying mechanical energy.
 21. Method according to any one of claims 1 to 20, characterized in that the work step includes manufacturing an optical or optoelectronic component or a color filter.
 22. Method according to any one of claims 1 to 21, characterized in that the work step includes manufacturing an electronic component.
 23. Method according to any one of claims 1 to 22, characterized in that the work step includes manufacturing a mechanical, chemical or biological sensor.
 24. Method according to any one of claims 1 to 23, characterized in that the work step includes manufacturing at least one active matrix and its address circuit (6, 6A, 6B, 6′, 6A′, 6B′, 26A, 26B), adapted so as to be integrated within a flat screen.
 25. Method according to any one of claims 1 to 24, characterized in that, after the work step, it additionally includes a covering step according to which a protective layer is deposited on the added layer incorporating the component.
 26. Method according to claim 25, characterized in that this protective layer is Si3N4.
 27. Method according to any one of claims 1 to 26, characterized in that, before the separation step, it additionally includes a joining step according to which an intermediate substrate (10) is affixed to the added layer and, after this separation step, a transfer step according to which this intermediate substrate is used to affix all or part of the thin layer to a final substrate (12).
 28. Method according to claim 27, characterized in that during the joining step, the thin layer is reversibly affixed to the intermediate substrate and after the transfer step, the thin layer is detached from the intermediate substrate.
 29. Method according to claim 27 or claim 28, characterized in that the final substrate is made from a different material from that of the initial substrate.
 30. Method according to any one of claims 27 to 29, characterized in that the final substrate is made from a material that is incompatible with the thermal conditions prevailing during the work step or those during the separation step.
 31. Method according to claim 29 or claim 30, characterized in that the final substrate is a plastic material.
 32. Method according to claim 31, characterized in that the final substrate is a transparent plastic material.
 33. Method according to claim 31 or claim 32, characterized in that the final substrate has a softening temperature below the maximum temperature of the work step.
 34. Method according to any one of claims 27 to 33, characterized in that a plurality of components is made during the work step and each component is individually affixed to its final substrate, having been detached from the rest of the thin layer.
 35. Method according to any one of claims 27 to 34, characterized in that the final substrate is a chip card.
 36. Method according to any one of claims 1 to 26, characterized in that, before the separation step, it additionally includes a joining step according to which the added layer is affixed to a final substrate.
 37. Method according to any one of claims 27 to 36, characterized in that the affixing on the final substrate is carried out by gluing or molecular adhesion.
 38. Method according to any one of claims 1 to 37, characterized in that a plurality of components is made during the treatment step and the fragile sub-layer is created facing the future components during the weakening step and the components are individually detached during the detachment step.
 39. Method according to any one of claims 1 to 38, characterized in that the preparation, weakening and work steps are applied to two substrates, these two substrates are assembled head to tail and the detachment steps are then applied to these two substrates.
 40. Application of the method according to any one of claims 1 to 37 to the manufacture of flat screens. 